This long-term project utilizing squirrel monkeys is concerned with identifying brain mechanisms involved in basic, communicative displays. Experiments involve testing the effects of various brain lesions on the highly predictable mirror display of gothic-type, male squirrel monkeys. The mirror display incorporates features of the challenge and courtship displays of these animals. The major result of the preceding work was the finding that the striatal complex (an evolutionary ancient and basic formation of the forebrain) plays an essential role in the expression of this display. Since the experiments involving pallidotegmental projections might have damaged monoaminergic systems arising in the isthmus region, the present experiments are being undertaken to learn whether or not elimination of respective isthmic cell groups containing serotonin and norepinephrine affect the performance of the display. In animals with lesions stereotaxically aimed at the ventral and dorsal raphe regions, respectively, there were no changes in display behavior. The anatomical findings are not yet available.